My research focuses on the neuronal and physiological mechanisms of peptidergic signaling. This proposal seeks to identify ligands for the remaining 17 orphan GPCRs that are predicted to have peptide ligands in Drosophila. I will clone receptor ORFs and functionally express them in HEK-293 cells. I will de-orphan these receptors with receptor desenstization, activation, internalization, and ligand binding assays. Of specific interest is the potential of identifying the GPCR that binds PDF and if so, secondary experiments are proposed to define the anatomical distribution and consequences of receptor manipulation on circadian output behaviors. I also propose to dissect the role(s) of receptor regulation in a defined behavior. I will make targeted disruptions in the corazonin receptor (CG10698), which has been implicated in clock regulation, to create receptor variants with differing signaling, desensitizing, and internalization properties. I will address e consequences of these manipulations on circadian output behaviors.